In non-destructive testing involving electromagnetic acoustic transducers (EMAT), it is preferable for the flaw to be struck at normal incidence (90 degrees) so that it can be better evaluated and characterized. Unfortunately, however, the wave generation of the transducers typically used are primarily bidirectional, but with some unidirectional characteristics, which hinders the achievement of this ideal because not all flaws are going to be perfectly aligned with the transducer. Thus these transducers are limited when used to inspect large areas.
In the past, non-destructive testing of large components with an EMAT required either multiple sensors at multiple orientations or it required repetitive scans. Multiple sensors were required so that a larger area could be covered per scan while the different orientations were necessary so that returning waves could decipher any flaw that may not be optimally orientated. The method of repetitive scanning necessitated many changes in the orientation of the sensors so that the flaw would be struck as optimally as possible.
As can be seen, each of the above methods try to direct their waves so as to strike and locate flaws as optimally as possible for better identification. While these methods are suitable for small surfaces, they become a burden when the object being tested is large or the time to inspect the workpiece is limited. Thus, utilizing such non-destructive testing methods on large surfaces is both cumbersome and time consuming due to the unidirectional or bidirectional wave generation of the transducers.
It is thus an object of this invention to provide an electromagnetic acoustic transducer whose wave generation is more than uni- or bidirectional. Another object of this invention is to provide a means of non-destructive testing that can cover large areas in a relatively small amount of time. Still another object of this invention is to provide a testing apparatus that will optimally strike the flaw for better identification. A further advantage of this invention is the fact that EMATs do not require an ultrasonic couplant and therefore the combination of an oscillating sensor with no couplant makes it ideal for rapid coverage in applications requiring automated inspections. These and other objects and advantages will become obvious upon further investigation.